UPTAKE AND DEGRADATION OF DESIALYLATED LUTEINIZING-HORMONE BY SUSPENDED HEPATOCYTES

The uptake and degradation of desialylated human luteinizing hormone (asialo-LH) in suspended [rat] hepatocytes were studied. Asialo-LH was taken up by the asialo-glycoprotein receptor at a rate which was somewhat lower than that of asialo-fetuin. The rate constants and equilibrium binding parameters were similar, but the rate of dissociation of the receptor-ligand complex was higher in the case of asialo-LH. The uptake was influenced by heterogeneity of the asialo-LH preparation. Degradation of endocytosed asialo-LH took place in the lysosomes. After fractionation of the cells by isopycnic centrifugation in a sucrose gradient, partially degraded asialo-LH (precipitable with trichloroacetic acid, but not with antibody) was found in the fractions containing endocytic vesicles, but not in the lysosomal fractions, indicating that the proteolysis of asialo-LH was initiated in the endocytic vesicles.